Name: measurement: si units and conversions
Uploaded: 2020-09-03T13:38:25.000Z
Duration: 3 min 38 s
Channel: JoVE

K12 Standards

ohios-learning-standards-and-model-curriculum

Ohio’s Learning Standards and Model Curriculum

9-12

Chemistry

Structure And Properties Of Matter

Quantifying matter

Measurement: Standard Units

Nella scienza, la misurazione è l'assegnazione di un valore numerico ad una caratteristica, come la massa, le dimensioni e la temperatura della materia. Ogni misurazione fornisce due tipi di informazioni. Il primo è il numero:la dimensione o l'ampiezza della misurazione.Il secondo è l'unità:uno standard di confronto per la misurazione. Quindi, quando diciamo che l'acqua bolle a 100°C, il numero 100 rappresenta l'ampiezza della misurazione, mentre C rappresenta l'unità. Insieme, trasmettono la dimensione relativa della proprietà della materia in questione:il punto di ebollizione.Senza unità, un numero può essere privo di significato o generare confusione. Per esempio, se l'altezza della Torre Eiffel viene riportata di 300, senza fornire le unità, il contesto del numero 300 non è chiaro. Ciò significa che la Torre Eiffel potrebbe essere relativamente alta o molto bassa.ma senza le unità di dimensione, la valutazione risulterebbe difficile. A volte viene fornita anche una terza forma di informazione:l'errore. Questi dati sono un'indicazione dell'incertezza della misurazione.Pertanto, al fine di misurare e riportare accuratamente le varie proprietà della materia, sono stati sviluppati comuni sistemi di misurazione. Il Sistema Internazionale di Unità, o sistema SI, è quello utilizzato universalmente dagli scienziati. Sotto il sistema SI, sono state fissate le unità di misura per 7 proprietà fondamentali:lunghezza, massa, tempo, temperatura, corrente elettrica, quantitativo di sostanza e intensità luminosa.Queste sono definite unità standard o unità di base. Di questi, le unità di base per le prime quattro proprietà sono quelle utilizzate più comunemente in chimica. L'unità standard di lunghezza nel sistema SI è il metro, rappresentato dal simbolo di unità m"Le distanze più lunghe sono spesso riportate in chilometri, o km"dove 1 chilometro equivale a 1000 metri.Al contrario, distanze più brevi possono essere riportate in centimetri, o cm"dove 1 centimetro equivale a 0, 01 metri;o in millimetri, mm"dove 1 millimetro equivale a 0, 001 metri. Allo stesso modo, l'unità standard di massa nel sistema SI è il chilogrammo, rappresentato dal simbolo dell'unità kg"Un chilogrammo equivale a 1000 grammi. La temperatura è un'altra proprietà fondamentale, con l'unità SI kelvin e il simbolo dell'unità K"in maiuscolo.Viene visualizzato senza la parola grado"o il simbolo del grado, per distinguerlo dai gradi Celsius e dai gradi Fahrenheit. Per esempio, l'acqua bolle a 373, 15 K e la temperatura normale del corpo umano è di circa 310 K.La quarta unità di base più comunemente usata è il secondo, l'unità di tempo SI, con il simbolo di unità s"Mentre intervalli di tempo più brevi possono essere espressi come millisecondi, dove 1 millisecondo è uguale a 0, 001 secondi, intervalli di tempo più lunghi possono essere espressi come megasecondi, dove 1 megasecondo equivale a 1 milione di secondi. In alternativa, vengono utilizzate anche unità non SI come ore, giorni e anni.

misure: unità standard

Ogni misura fornisce tre tipi di informazioni: la dimensione o l'entità della misurazione (un numero), uno standard di confronto per la misurazione (un'unità) e un'indicazione dell'incertezza della misurazione. Mentre il numero e l'unità sono rappresentati esplicitamente quando una quantità è scritta, l'incertezza è un aspetto degli errori nei risultati di misurazione.

Il numero nella misura può essere rappresentato in modi diversi, tra cui la forma decimale e la notazione scientifica, che è anche nota come notazione esponenziale. Ad esempio, il peso massimo al decollo di un aereo di linea Boeing 777-200ER è di 298.000 chilogrammi, che può anche essere scritto come 2,98 × 105 kg.

Le unità, come litri, libbre e centimetri, sono standard di confronto per le misurazioni. Una bottiglia da 2 litri di una bibita analcolica contiene un volume di bevande che è il doppio di quello del volume accettato di 1 litro. Senza unità, un numero può essere privo di significato, confuso o forse pericoloso per la vita. Supponiamo che un medico prescriva fenobarbital per controllare le convulsioni di un paziente e inscriva un dosaggio di "100" senza specificare le unità. Non solo questo sarà fonte di confusione per il professionista medico che dà la dose, ma le conseguenze possono essere terribili: 100 mg somministrati tre volte al giorno possono essere efficaci come anticonvulsivonte, ma una singola dose di 100 g è più di 10 volte la quantità letale.

<h4>Il Sistema internazionale di unità di misura (unità SI)</h4>

Le unità di misura per sette proprietà fondamentali ("unità di base"): lunghezza, massa, tempo, temperatura, corrente elettrica, quantità di sostanza e intensità luminosa, sono state fissate di comune accordo internazionale. Sono chiamati Sistema Internazionale di Unità o Unità SI. Le unità per altre proprietà possono essere derivate da queste sette unità di base. Le unità di misura quotidiane sono spesso definite come frazioni o multipli di altre unità. Il latte è comunemente confezionato in contenitori da 1 gallone (4 litri), 1 quarto (0,25 galloni) e una pinta (0,5 litri). Questo stesso approccio viene utilizzato con le unità SI, ma queste frazioni o multipli sono sempre potenze di 10. Le unità SI frazionarie o multiple sono denominate utilizzando un prefisso e il nome dell'unità di base. Ad esempio, una lunghezza di 1000 metri è anche chiamata chilometro perché il prefisso kilo significa "mille", che nella notazione scientifica è 103 (1 chilometro = 1000 m = 103 m).

<h4>Unità SI standard</h4>

Le unità iniziali del sistema metrico, che alla fine si evolsero nel sistema SI, furono stabilite in Francia durante la Rivoluzione francese. Le norme originali per il contatore e il chilogrammo furono adottate lì nel 1799 e infine da altri paesi. Le seguenti sono le quattro unità di base SI comunemente utilizzate in chimica.

<h4>1. Lunghezza</h4>

L'unità standard di lunghezza nel sistema SI è il misuratore (m). Un metro è definito come la distanza che la luce percorre nel vuoto in 1/299.792.458 di secondo. Distanze più lunghe sono spesso segnalate in chilometri (1 km = 1000 m = 103 m), mentre distanze più brevi possono essere segnalate in centimetri (1 cm = 0,01 m = 10−2 m) o millimetri (1 mm = 0,001 m = 10−3 m).

<h4>2. Messa</h4>

L'unità di massa standard nel sistema SI è il chilogrammo (kg). Un chilogrammo è definito dalla massa di un oggetto di riferimento - un cilindro metallico realizzato in lega platino-iridio con un'altezza e un diametro di 39 mm. Si dice che qualsiasi oggetto con la stessa massa di questo riferimento abbia una massa di 1 chilogrammo. Il grammo (g) è esattamente uguale a 1/1000 della massa del chilogrammo (10−3 kg).

Il termine "peso" è spesso usato in modo intercambiabile con "massa". Tuttavia, le due quantità sono diverse. Mentre la massa di un oggetto misura la quantità di materia al suo interno, il suo peso misura la forza gravitazionale esercitata sulla sua materia. Per esempio, se potessimo pesarci sulla luna, che ha una gravità più debole della Terra, peseremo meno di quanto abbiamo fatto sulla Terra. Tuttavia, la massa, la quantità di materia nel nostro corpo, rimarrebbe la stessa.

<h4>3. Temperatura</h4>

L'unità di temperatura SI è il kelvin (K), anche se il grado Celsius (°C) è consentito anche nel sistema SI, sia con la parola "grado" che con il simbolo di grado utilizzato per le misurazioni Celsius. I gradi Celsius hanno la stessa grandezza di quelli di kelvin, ma le due scale posizionano i loro zeri in luoghi diversi. L'acqua congela a 273,15 K (0 °C) e bolle a 373,15 K (100 °C) per definizione e la temperatura normale del corpo umano è di circa 310 K (37 °C). La scala Fahrenheit (°F) è un'altra unità comunemente usata per misurare la temperatura. Sulla scala Fahrenheit, l'acqua si congela a 32 ° F e bolle a 212 ° F e la normale temperatura corporea umana è di 96 ° F.

Mentre le scale di Fahrenheit e Celsius consentono temperature negative, la scala di Kelvin, chiamata anche scala assoluta, non lo fa. Sulla scala di Kelvin, 0 K è la temperatura più bassa, che è nota come zero assoluto.

Le scale di temperatura sono interconvertibili utilizzando le seguenti formule di conversione:

<img alt="Eq1" src="https://www.jove.com/files/core/CDNSource/lessons/1010/1010_Equations-01.png" style="height: 40px;">

<img alt="Eq2" src="https://www.jove.com/files/core/CDNSource/lessons/1010/1010_Equations-02.png" style="height: 40px;">

<h4>4. Tempo</h4>

L'unità di base del tempo SI è la seconda o le seconde. Intervalli di tempo piccoli e grandi possono essere espressi con i prefissi appropriati. Per esempio:

<img alt="Eq3" src="https://www.jove.com/files/core/CDNSource/lessons/1010/1010_Equations-03.png" style="height: 40px;">

<img alt="Eq4" src="https://www.jove.com/files/core/CDNSource/lessons/1010/1010_Equations-04.png" style="height: 40px;">

In alternativa, è possibile utilizzare ore, giorni e anni.

Questo testo è adattato da <a href="https://openstax.org/books/chemistry-2e/pages/1-4-measurements">Openstax, Chimica 2e, Sezione 1.4: Misure.</a>

Misure: unità standard

Ogni misurazione fornisce tre tipi di informazioni: la dimensione o l'entità della misurazione (un numero), uno standard di confronto per la misurazione ...

Education

Didattica

JoVE Core

Chimica

Introduction: Matter and Measurement

Introduzione: Materia e Misurazione

KEY TERMS AND CONCEPTS

TERMINI E CONCETTI CHIAVE

measurement: si units and conversions

Measurement gives three kinds of information: a number, a unit, and an estimate of uncertainty. The number shows size or magnitude. The unit gives a standard for comparison. The uncertainty reflects possible error in the measurement.

Numbers can be written in more than one way. A value may appear in decimal form or in scientific notation, which is also called exponential notation. For example, the maximum take-off weight of a Boeing 777-200ER airliner is 298,000 kilograms, or 2.98 × 10^5 kg.

Units are essential because they make a number meaningful. Common units such as liters, pounds, and centimeters help people compare measurements. A 2-liter bottle of soft drink contains twice the volume of a 1-liter bottle. Without units, a number can be confusing or even dangerous. A doctor who writes a dose as “100” without units could create a serious mistake, because 100 mg taken three times a day can be effective, while 100 g is more than 10 times the lethal amount.

The International System of Units, or SI units, is based on seven fundamental properties called base units. These properties are length, mass, time, temperature, electric current, amount of substance, and luminous intensity. Other units are derived from these base units. Everyday units often use fractions or multiples of a base unit, and SI units do the same with powers of 10. Prefixes show these multiples. For example, kilo means one thousand, so 1 kilometer equals 1000 meters, or 10^3 m.

The metric system began in France during the French Revolution. The original standards for the meter and kilogram were adopted in 1799 and later used by other countries. In chemistry, the four SI base units used most often are length, mass, temperature, and time.

The SI unit of length is the meter, or m. A meter is defined as the distance light travels in a vacuum in 1/299,792,458 of a second. Longer distances are often given in kilometers, while shorter distances are often given in centimeters or millimeters. These units relate directly to the meter: 1 km = 1000 m = 10^3 m, 1 cm = 0.01 m = 10^-2 m, and 1 mm = 0.001 m = 10^-3 m.

The SI unit of mass is the kilogram, or kg. It is defined by a reference object, a metal cylinder made from platinum-iridium alloy with a height and diameter of 39 mm. Any object with the same mass as that reference has a mass of 1 kilogram. The gram, or g, is exactly 1/1000 of a kilogram, which is 10^-3 kg. Weight is often used like mass, but they are not the same. Mass is the amount of matter in an object, while weight is the gravitational force on that matter. That is why a person would weigh less on the moon, where gravity is weaker, but the mass would stay the same.

The SI unit of temperature is the kelvin, or K, although degree Celsius, or °C, is also allowed in SI. Celsius and kelvin have the same size unit, but their zero points are different. Water freezes at 273.15 K, which is 0 °C, and boils at 373.15 K, which is 100 °C. Normal human body temperature is about 310 K, or 37 °C. Fahrenheit, or °F, is another common scale. On that scale, water freezes at 32 °F and boils at 212 °F, and normal body temperature is 96 °F. Celsius and Fahrenheit can show negative temperatures, but Kelvin cannot. The Kelvin scale starts at 0 K, called absolute zero. Temperature scales can be converted using the given formulas.

The SI base unit of time is the second, or s. Small and large time intervals can be written with prefixes, and hours, days, and years are also used. Together, these units help scientists and students describe measurements clearly and compare results with confidence.

Measurement: SI Units and Conversions

scientific laws and theories

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Distinguishing Physical and Chemical Changes

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States of matter help describe how matter behaves in chemistry. Matter is anything that has mass and takes up space. It is found everywhere, including air, water, soil, mountains, and even our bodies. The three common states on Earth are solid, liquid, and gas. A solid has a definite shape and a definite volume. Its particles, such as atoms or molecules, are packed very closely together and held in place by strong forces, so they only vibrate slightly. This tight arrangement makes solids...

measurement: standard units

Measurement gives three kinds of information: a number, a unit, and an estimate of uncertainty. The number shows size or magnitude. The unit gives a standard for comparison. The uncertainty reflects possible error in the measurement. Numbers can be written in more than one way. A value may appear in decimal form or in scientific notation, which is also called exponential notation. For example, the maximum take-off weight of a Boeing 777-200ER airliner is 298,000 kilograms, or 2.98 × 10^5 kg. <br...

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measurement: derived units

SI Units, Density, and Property Types

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uncertainty in measurement: accuracy and precision

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key terms and concepts

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Measurement: SI Units and Conversions | JoVE K12

chemistry

JoVE Core: Chimica illustra concetti chiave di chimica attraverso video animazioni concise e di immediata comprensione. Inoltre, i video della sezione "scienziati in azione" mostrano procedure metodologiche realizzate da ricercatori provenienti dai migliori laboratori internazionali.

Texas Essential Knowledge and Skills

High School

Specialised Topic in Science

112.51.c.1.

112.51.c.1.E.

CHEM.1

CHEM.1.E

Biology

BIO.1

BIO.1.E

The Atomic Theory of Matter

The earliest recorded discussion of the basic structure of matter comes from ancient Greek philosophers. Leucippus and Democritus argued that all matter ...

The Bohr Model

Following the work of Ernest Rutherford and his colleagues in the early twentieth century, the picture of atoms consisting of tiny dense nuclei surrounded ...

The Quantum-Mechanical Model of an Atom

Shortly after de Broglie published his ideas that the electron in a hydrogen atom could be better thought of as being a circular standing wave instead of ...

Subatomic Particles

Dalton was only partially correct about the particles that make up matter. All matter is composed of atoms, and atoms are composed of three smaller ...

Quantum Numbers

It is said that the energy of an electron in an atom is quantized; that is, it can be equal only to certain specific values and can jump from one energy ...

Atomic Orbitals

An atomic orbital represents the three-dimensional regions in an atom where an electron has the highest probability to reside. The radial distribution ...

The Pauli Exclusion Principle

The arrangement of electrons in the orbitals of an atom is called its electron configuration. We describe an electron configuration with a symbol that ...

The Energies of Atomic Orbitals

In an atom, the negatively charged electrons are attracted to the positively charged nucleus. In a multielectron atom, electron-electron repulsions are ...

The Aufbau Principle and Hund's Rule

To determine the electron configuration for any particular atom, we can build the structures in the order of atomic numbers. Beginning with hydrogen, and ...

electron-configuration-of-multielectron-atoms

Electron Configuration of Multielectron Atoms

The alkali metal sodium (atomic number 11) has one more electron than the neon atom. This electron must go into the lowest-energy subshell available, the ...

Thomson's e/m Experiment

In a beam of charged particles created by a heated cathode, the particles move at different speeds. However, many applications need a beam with uniform ...

Atomic structure
• Evolution of atomic models/theory
• Electrons
• Electron configurations

Content elaboration: Physical Science included properties and locations of protons, neutrons and electrons, atomic number, mass number, cations and anions, isotopes and the strong nuclear force which holds the nucleus together. In this course, the historical development of the atomic model and the positions of electrons are explored in greater detail. Atomic models are constructed to explain experimental evidence and make predictions. The changes in the atomic model over time exemplify how scientific knowledge changes as new evidence emerges and how technological advancements like electricity extend the boundaries of scientific knowledge. Thompson's study of electrical discharges in cathode-ray tubes led to the discovery of the electron and the development of the plum pudding model of the atom. Rutherford's experiment, in which he bombarded gold foil with a-particles, led to the discovery that most of the atom consists of empty space with a relatively small, positively charged nucleus. Bohr used data from atomic spectra to propose a planetary model of the atom in which electrons orbit the nucleus, like planets around the sun. Later, Schrödinger used the idea that electrons travel in waves to develop a model in which electrons travel randomly in regions of space called orbitals (quantum mechanical model). Based on the quantum mechanical model, it is not possible to predict exactly where electrons are located but there is a region of space surrounding the nucleus in which there is a high probability of finding an electron (electron cloud or orbital). Data from atomic spectra (emission and absorption) gives evidence that electrons can only exist at certain discrete energy levels and not at energies between these levels. Atoms are usually in the ground state where the electrons occupy orbitals with the lowest available energy. However, the atom can become excited when the electrons absorb a photon with the precise amount of energy (indicated by the frequency of the photon) to move to an orbital with higher energy. Any photon without this precise amount of energy will be ignored by the electron. The atom exists in the excited state for a very short amount of time. When an electron drops back down to the lower energy level, it emits a photon that has energy equal to the energy difference between the levels. The amount of energy is indicated by the frequency of the light that is given off and can be measured. Each element has a unique emission and absorption spectrum due to its unique electron configuration and specific electron energy jumps that are possible for that element. Being aware of the quantum mechanical model as the currently accepted model for the atom is important for science literacy as it explains and predicts subatomic interactions, but details should be reserved for more advanced study. Electron energy levels consist of sublevels (s, p, d and f), each with a characteristic number and shape of orbitals. Orbital diagrams and electron configuration can be constructed to show the location of the electrons in an atom using established rules. Valence electrons are responsible for most of the chemical properties of elements. In this course, electron configuration (extended and noble gas notation) and orbital diagrams can be shown for any element in the first three periods. Although the quantum mechanical model of the atom explains the most experimental evidence, other models can still be helpful. Thinking of atoms as indivisible spheres is useful in explaining many physical properties of substances, such as the state (solid, liquid or gas) of a substance at room temperature. Bohr's planetary model is useful to explain and predict periodic trends in the properties of elements.

Atomic structure

The Periodic Table

As early chemists discovered more elements, they realized that various elements could be grouped by their similar chemical behaviors. One such grouping ...

Periodic Classification of the Elements

The periodic table arranges atoms based on increasing atomic number so that elements with the same chemical properties recur periodically. When their ...

atomic-radii-and-effective-nuclear-charge

Atomic Radii and Effective Nuclear Charge

The elements in groups of the periodic table exhibit similar chemical behavior. This similarity occurs because the members of a group have the same number ...

Ionic Radii

Ionic radius is the measure used to describe the size of an ion. A cation always has fewer electrons and the same number of protons as the parent atom; it ...

Ionization Energy

The amount of energy required to remove the most loosely bound electron from a gaseous atom in its ground state is called its first ionization energy ...

Electron Affinity

The electron affinity (EA) is the energy change for adding an electron to a gaseous atom to form an anion (negative ion).



This process can be either ...

Alkali Metals

Group 1 elements are soft and shiny metallic solids. They are malleable, ductile, and good conductors of heat and electricity. The melting points of the ...

Halogens

Group 17 elements, known as halogens, are nonmetals. At room temperature, fluorine and chlorine are gases, bromine is a liquid, and iodine a solid. ...

Noble Gases


The elements in group 18 are noble gases (helium, neon, argon, krypton, xenon, and radon). They earned the name &ldquo;noble&rdquo; because they were ...

Periodic Table
• Properties
• Trends

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Periodic Table

Types of Chemical Bonds

Chemical bonding theories were pioneered by American chemist Gilbert&#xA0;N. Lewis. He developed a model called the Lewis model to explain the type and ...

Lewis Symbols and the Octet Rule

Chemical bonds are complex interactions between two or more atoms or ions, which reduce the potential energy of the molecule. Gilbert N. Lewis developed a ...

Ionic Bonding and Electron Transfer

Ions are atoms or molecules bearing an electrical charge. A cation (a positive ion) forms when a neutral atom loses one or more electrons from its valence ...

The Born-Haber Cycle

Lattice Energy&#xA0;

An ionic compound is stable because of the electrostatic attraction between its positive and negative ions. The lattice energy of a ...

trends-in-lattice-energy-ion-size-and-charge

Trends in Lattice Energy: Ion Size and Charge

An ionic compound is stable because of the electrostatic attraction between its positive and negative ions. The lattice energy of a compound is a measure ...

Covalent Bonding and Lewis Structures

Compared to ionic bonds, which results from the transfer of electrons between metallic and nonmetallic atoms, covalent bonds result from the mutual ...

Electronegativity

Whether a bond is nonpolar or polar covalent is determined by a property of the bonding atoms called electronegativity.&#xA0;

Electronegativity values of ...

bond-polarity-dipole-moment-and-percent-ionic-character

Bond Polarity, Dipole Moment, and Percent Ionic Character

Bond Polarity

The absolute value of the difference in electronegativity (&Delta;EN) of two bonded atoms provides a rough measure of the polarity to be ...

lewis-structures-of-molecular-compounds-and-polyatomic-ions

Lewis Structures of Molecular Compounds and Polyatomic Ions

To draw Lewis structures for complicated molecules and molecular ions, it is helpful to follow a step-by-step procedure as outlined:


	Determine the ...

Resonance

The Lewis structure of a nitrite anion (NO2&minus;) may actually be drawn in two different ways, distinguished by the locations of the N-O and N=O ...

Formal Charges

In some cases, there are seemingly more than one valid Lewis structures for molecules and polyatomic ions. The concept of formal charges can be used to ...

Exceptions to the Octet Rule

Many covalent molecules have central atoms that do not have eight electrons in their Lewis structures. These molecules fall into three categories:


	...

Bond Energies and Bond Lengths

Stable molecules exist because covalent bonds hold the atoms together. The strength of a covalent bond is measured by the energy required to break it, ...

VSEPR Theory and the Basic Shapes

Overview of VSEPR Theory

Valence shell electron-pair repulsion theory (VSEPR theory) enables us to predict the molecular structure, including approximate ...

vsepr-theory-and-the-effect-of-lone-pairs

VSEPR Theory and the Effect of Lone Pairs

Effect of Lone Pairs of Electrons&nbsp;on Molecule Geometry

It is important to note that electron-pair geometry around a central atom is not the same ...

Predicting Molecular Geometry

VSEPR Theory for Determination of Electron Pair Geometries

The following procedure uses VSEPR theory to determine the electron pair geometries and the ...

Molecular Shape and Polarity

Dipole Moment of a Molecule

Polar covalent bonds connect two atoms with differing electronegativities, leaving one atom with a partial positive charge ...

Valence Bond Theory

Overview of Valence Bond Theory

Valence bond theory describes a covalent bond as the overlap of half-filled atomic orbitals (each containing a single ...

Hybridization of Atomic Orbitals I

The mathematical expression known as the wave function, &#x3C8;, contains information about each orbital and the wavelike properties of electrons in an ...

Hybridization of Atomic Orbitals II

sp3d and sp3d&nbsp;2 Hybridization

To describe the five bonding orbitals in a trigonal bipyramidal arrangement, we must use five of the valence shell ...

Molecular Orbital Theory I

Overview of Molecular Orbital Theory

Molecular orbital theory describes the distribution of electrons in molecules in the same way as the distribution of ...

Molecular Orbital Theory II

Molecular Orbital Energy Diagrams

The relative energy levels of atomic and molecular orbitals are typically shown in a molecular orbital diagram. For a ...

Bonding in Metals

Metallic bonds are formed between two metal atoms. A simplified model to describe metallic bonding has been developed by Paul Dr&#xFC;de called the ...

Chemical bonding
• lonic
• Polar/covalent

Content elaboration: Content in the Physical Science course included recognizing that atoms with unpaired electrons tend to form ionic and covalent bonds with other atoms, forming molecules, ionic lattices or network covalent structures. In this course, electron configuration, electronegativity values and energy considerations will be applied to bonding and the properties of materials with different types of bonding. Atoms of many elements are more stable when they are bonded to other atoms. In such cases, as atoms bond, energy is released to the surroundings, resulting in a system with lower energy. An atom's electron configuration, particularly the valence electrons, determines how an atom interacts with other atoms. Molecules, ionic lattices and network covalent structures have different, yet predictable, properties that depend on the identity of the elements and the types of bonds formed. Differences in electronegativity values can be used to predict where a bond fits on the continuum between ionic and covalent bonds. The polarity of a bond depends on the electronegativity difference and the distance between the atoms (bond length). Polar covalent bonds are introduced as an intermediary between ionic and pure covalent bonds. The concept of metallic bonding is also introduced to explain many of the properties of metals (e.g., conductivity). Since most compounds contain multiple bonds, a substance may contain more than one type of bond. Carbon atoms can bond together and with other atoms, especially hydrogen, oxygen, nitrogen and sulfur, to form chains, rings and branching networks that are present in a variety of important compounds, including synthetic polymers, fossil fuels and the large molecules essential to life.

Chemical bonding

Chemical Formulas

A chemical formula presents information about the proportions of atoms constituting a particular chemical compound or molecule, mainly using symbols of ...

ionic-compounds-formulas-and-nomenclature

Ionic Compounds: Formulas and Nomenclature

An element composed of atoms that readily lose electrons (a metal) can react with an element composed of atoms that readily gain electrons (a nonmetal) to ...

molecular-compounds-formulas-and-nomenclature

Molecular Compounds: Formulas and Nomenclature

Molecular compounds or covalent compounds result when atoms share electrons to form covalent bonds. Since there is no electron transfer, molecular ...

Organic Compounds

All living things are formed mostly of carbon compounds called organic compounds. The category of organic compounds includes both natural and synthetic ...

Classification of Elements and Compounds

Pure substances consist of only one type of matter. A pure substance can be an element or a compound. An element consists of only one type of atom, while ...

Molecular Models

Physical models representing molecular architectures of chemical compounds play essential roles in understanding chemistry. The use of molecular models ...

Representing compounds
• Formula writing
• Nomenclature
• Models and shapes (Lewis structures, ball and stick, molecular geometries)

Content elaboration: Using the periodic table, formulas of ionic compounds containing specific elements can be predicted. This can include ionic compounds made up of elements from groups 1, 2, 17, hydrogen, oxygen and polyatomic ions (given the formula and charge of the polyatomic ion). Given the formula, a compound can be named using conventional systems that include Greek prefixes and Roman numerals where appropriate. Given the name of an ionic or covalent substance, formulas can be written. Many different models can be used to represent compounds including chemical formulas, Lewis structures, and ball and stick models. These models can be used to visualize atoms and molecules and to predict the properties of substances. Each type of representation provides unique information about the compound. Different representations are better suited for particular substances. Lewis structures can be drawn to represent covalent compounds using a simple set of rules and can be combined with valence shell electron pair repulsion (VSEPR) theory to predict the three-dimensional electron pair and molecular geometry of compounds. Lewis structures and molecular geometries will only be constructed for the following combination of elements: hydrogen, carbon, nitrogen, oxygen, phosphorus, sulfur and the halogens.

Representing compounds

Every measurement provides three kinds of information: the size or magnitude of the measurement (a number), a standard of comparison for the measurement ...

Measurement: Derived Units

The International System of Units or SI system, by international agreement, has fixed measurement units for seven fundamental properties: length, mass, ...

Uncertainty in Measurement: Accuracy and Precision

Scientists typically make repeated measurements of a quantity to ensure the quality of their findings and to evaluate both the precision and the accuracy ...

Uncertainty in Measurement: Reading Instruments

Counting is the type of measurement that is free from uncertainty, provided the number of objects being counted does not change during the process. Such ...

Uncertainty in Measurement: Significant Figures

All the digits in a measurement, including the uncertain last digit, are called significant figures or significant digits. Note that zero may be a ...

Quantifying matter

Content elaboration: In earlier grades, properties of materials were quantified with measurements that were always associated with some error. In this course, scientific protocols for quantifying the properties of matter accurately and precisely are studied. Using the International System of Units (SI), significant digits or figures, scientific notation, error analysis and dimensional analysis are vital to scientific communication. There are three domains of magnitude in size and time: the macroscopic (human) domain, the cosmic domain and the submicroscopic (atomic and subatomic) domain. Measurements in the cosmic domain and submicroscopic domains require complex instruments and/or procedures. Matter can be quantified in a way that macroscopic properties such as mass can reflect the number of particles present. Elemental samples are a mixture of several isotopes with different masses. The atomic mass of an element is calculated given the mass and relative abundance of each isotope of the element as it exists in nature. Because the mass of an atom is very small, the mole is used to translate between the atomic and macroscopic levels. A mole is equal to the number of atoms in exactly 12 grams of the isotope carbon-12. The mass of one mole of a substance is equal to its molar mass in grams. The molar mass for a substance can be used in conjunction with Avogadro's number and the density of a substance to convert between mass, moles, volume and number of particles of a sample.

Measurement: SI Units and Conversions

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